Reflecting member and flame sensor

1:

• A reflecting member made from a tube-shaped member having an inner peripheral surface, the reflecting member comprising:
• a reflecting surface structured with the inner peripheral surface formed symmetrically on an axis of the tube-shaped member, wherein
• a slope, relative to the axis, of a tangent line of the inner peripheral surface in a cross-sectional plane that contains the axis changes monotonically along the axis, and
• in relation to a target that is positioned facing a smaller opening of the tube-shaped member, positioned at a specific distance of separation therefrom, and having a flat region that is perpendicular to the axis and that is axially symmetrical relative to the axis, of an electromagnetic radiation that is incident along the axis from a larger opening of the tube-shaped member and is reflected by the inner peripheral surface, that electromagnetic radiation that is reflected at a specific location on the larger opening side is incident on one end side of the flat region, and that electromagnetic radiation that is reflected from a specific location on the smaller opening side is incident on the other end side of the flat region.